A two stroke diesel engines and four stroke diesel engines that include variable valve timing may operate with relatively large amounts of residual exhaust gas that has been left in engine cylinders from earlier combustion events in the engine cylinders. These same engines may include a particulate filter in their exhaust systems to trap carbonaceous soot that may be produced as a byproduct of combustion. Over a period of time, the particulate filter may fill with soot such that it may provide a more significant restriction to exhaust gases. The particulate filter may be regenerated via increasing exhaust gas temperature and supplying an oxygen rich exhaust mixture to the particulate filter such that soot held within the particulate filter combusts, thereby regenerating the particulate filter. The exhaust gas temperature may be increased via injecting post fuel injection amounts into the cylinder that may be expelled to the engine's exhaust system where the fuel may combust within an oxidation catalyst and raise exhaust gas temperatures. However, some of the post injected fuel may be retained within engine cylinders where it may combust during a next cycle of a cylinder. The retained fuel may increase engine torque and facilitate combustion timing that is earlier than is desired. Therefore, it may be desirable to estimate an amount of fuel residual that is in an engine cylinder from one cylinder cycle to a next cylinder cycle.
The inventors herein have recognized the above-mentioned challenges and have developed an engine control method, comprising: estimating an amount of fuel held in a cylinder from a first cycle of the cylinder to a second cycle of the cylinder via a controller in response to a temperature increase of an oxidation catalyst; and adjusting an amount of fuel injected to the cylinder via the controller during the second cycle of the cylinder in response to the estimated amount of fuel.
By estimating an amount of fuel retained in a cylinder from one cylinder cycle to a next cylinder cycle in response to a catalyst temperature, it may be possible to adjust fuel injection during the next cylinder cycle in a way that provides accurate engine torque delivery and reduced emissions. The catalyst temperature may provide an accurate estimate of fuel retained in the cylinder without having to know cylinder pressure. In particular, post injected fuel that has not participated in combustion and that has been ejected from engine cylinders to facilitate particulate filter regeneration increases catalyst temperature. The catalyst temperature increase is a function of the post injected amount of fuel that has not participated in combustion within the cylinder and that has been ejected from the cylinder. The amount of post injected fuel retained in the cylinder from one cycle of the cylinder to the next cycle of the cylinder is the post injected amount of fuel minus the amount of fuel that has not participated in combustion within the cylinder and that has been ejected from the cylinder.
The present description may provide several advantages. Specifically, the approach may estimate an amount of post injected fuel that is retained in a cylinder from a cylinder cycle to a next cylinder cycle without having to know pressure within the cylinder. Further, the approach provides ways of adjusting fuel injection timing to improve engine torque control and engine emissions. In addition, the approach may help to improve control of exothermic reactions within an oxidation catalyst during particulate filter regeneration.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.